Human development
Day 1: fertilization: all human chromosomes are present; unique human life begins. Day 6: embryo begins implantation in the uterus. Day 22: heart begins to beat with the child's own blood, often a different type than the mothers'. Week 3: By the end of third week the child's backbone spinal column and nervous system are forming. The liver, kidneys and intestines begin to take shape. Week 4: By the end of week four the child is ten thousand times larger than the fertilized egg. Week 5: Eyes, legs, and hands begin to develop. Week 6: Brain waves are detectable; mouth and lips are present; fingernails are forming. Week 7: Eyelids, and toes form, nose distinct. The baby is kicking and swimming. Week 8: Every organ is in place, bones begin to replace cartilage, and fingerprints begin to form. By the 8th week the baby can begin to hear. Weeks 9 and 10: Teeth begin to form, fingernails develop. The baby can turn his head, and frown. The baby can hiccup. Weeks 10 and 11: The baby ...